1. Field of the Invention
The present invention relates to the transport of stacks of printed sheets and, particularly, to the conveyance of collated printed matter which may vary significantly in stack thickness. More specifically, this invention is directed to conveyor systems for loosely stacked products which are received with defined cyclical intervals and which may experience large differences in stack thickness and, especially, to such conveyor systems wherein the direction of motion of the received products may be altered to divert defective products from a main stream. Accordingly, the general object of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in the movement of loosely stacked products such as, for example, collated sheets of printed material. Belt conveyor systems for moving loosely stacked products between work stations, for example in palletizing installations, are known in the art. Such prior art systems typically have a linearly extending continuous belt conveyor, in the form of an ascending band, and a cooperating continuous belt which functions as a top or clamping band. Such systems may also include a plurality of spring-mounted pressure rollers which act on one of the belts.
Belt conveyor systems of the type generally and briefly described above have also been used for separating incorrectly gathered stacks of printed sheets from a transport channel which leads between a collating machine and a downstream processing machine. Such separating conveyor systems include cooperating bottom and top belt conveyors which extend obliquely with respect to the transport channel and, in response to a command signal provided by a monitoring device, may be caused to intercept and take over the transport of defective stacks. The operation of such prior art separating devices is based upon, and permitted by, the fact that the stacks of printed sheets are fed from the gathering machine at cyclical intervals. Accordingly, a defective stack may be intercepted, clamped between the bottom and top belt conveyors of the separating system and delivered to a discharge conveyor.
In the prior art, the operationally reliable conveying of products such as stacks of printed sheets has been possible only when the deviations in stack thickness fall within a relatively narrow range and when there is at least a predetermined degree of friction between the individual sheets comprising the stacks. A lack of sufficient friction between the sheets will, particularly in the case of a fault which causes an increase in stack thickness, lead to shifting of the sheets relative to one another with resultant stack misalignment or collapse. If the deviations in stack thickness are too large, a stack will either not be clamped between the top and bottom belts of the separating conveyor system or the top and bottom belts of the conveyor system will be too closely spaced to accept the in-coming stack. Any loss of alignment within a stack or failure to receive and engage a stack by the conveyor system will result in production line stoppage with all of the undesirable consequences incident thereto.